Production of finely divided metals



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PRODUCTION OF FINELY DIVIDED METALS Filed March 4, 1930 1: e0 ,jciaZeohb WaZZe/"507zz&&ard& v INVEN TORS A TTORNEYS.

Patented Dec. 15, 1931 UNITED STATES PATENT OFFICE LEO SCHLECHT, OF LUDW'IGSHAFEN-ON-THERHINE, AND WALTER SCHUIBARDT, OI

MANNHEIM, GERMANY, ASSIGN'ORS TO I. G. FARBENINDUSTRIE AKTIENGESELL- SGHAFT, OF FRANKFORT-ON-THE-MAIN, GERMANY PRODUCTION OF FINELY DIVIDED METALS Application filed March 4, 1930, Serial No.'4=33,1 70,and in Germany March 5, 1929.

The present invention relates to the production of finely divided metals and more particularly to improvements in that process of thermally decomposing metal carbonyls in which the metal carbonyl is thermally decomposed by introducing it, diluted, if desired, with inert gases, into a heated vessel in such a manner that the decomposition takes place substantially in the hot free space of the vessle instead of by contact with the hot walls of the vessel. In the said process the temperature of the walls of the vessel should not eX- ceed a certain value since otherwise a substantial decomposition of carbon monoxide and in consequence a considerable contamination of the metal powder bv deposited carbon may take place. It has therefore been recommended to effect the decomposition of the metal carbonyl either at between about 100 and 400 C. or at about 900 C. or more. From an economical point of view, it is advisable to work in the lower ofthe temperature ranges indicated, and the present invention is concerned more particularly with operations carried out in this range of temperatures. Since the decomposition of metal carbonyls is an endothermic reaction, it is essential that sufficient heat is supplied to the carbonyl vapor to be decomposed.

' In the said method of working there is always the risk that due to an insufiicient supply of heat more or less substantial amounts of the metal produced are deposited in a compact form on the hot parts of the decomposition apparatus.

We have found that this undesirable formation of compact metal during the decom-.

position of the carbonyl is practically avoided and a metal powder which is uniform in composition and in the size of its particles, is obtained by keeping the temperature of those parts of the apparatus in which the decomposition of the carbonyl takes place substantially higher than the temperature at which the decomposition of the metal carbonyl is actually carried out in the free space of the vessel.

We have observed that deposits are very readily formed on theparts of the apparatus which come into contact with the carbonyl and these deposits quickly increase in size when the temperature of the said hot parts lies directly above the temperature in the free space of the vessel, but that on the contrary these deposits are no longer formed, but a powdery or spongy finely divided metal 1s formed when the temperature of the hot parts of the apparatus is substantially higher.

The amount to which the temperature must be raised in order to avoid the nudeslrable deposits is dependent on the decomposition conditions for the time being, for example on the dimensions and shape of the decomposition apparatus, on the size of the throughput of carbonyl and the like. It is preferable to provide the hot parts of the decomposition apparatus with smooth highly cerned.

Another way of facilitating the transfer of heat from the hot walls of the vessel to the carbonyl vapor to be decomposed consists 1n sub ecting the substances present in the decomposition chamber to a whirling or like motion.

This whirling may be efi'ected with a special apparatus built into the decomposition chamber, for example with a stirrer, which is preferably cooled from the inside in order to avoid any separation of the metal thereon. Also by suitably introducing a stream of gas or vapor, which if desired may be heated, or also by tangential introduction of the carbonyl into the decomposition chamber, a mixing of the hot layer of gas and vapor in the neighbourhood of the walls with the colder layers in the middle of the chamber is effected, so that the equalization of heat is accelerated and a more rapid removal of heat from the heated walls to the interior of the furnace is rendered possible.

In this manner of working there is no risk of solid" coherent deposits of metal being formed on the walls ofv the decompositionvessel, provided the intensity of the whirling, stirring or like motion is suitably adjusted. This is probably due to the fact that there exists an extremely thin layer of carbon monoxide on the hot walls which, when proper working conditions are employed, prevents the carbonyl from coming into direct contact with the walls. Only by whirlin or stirring too intensely, the said layer of carbon monoxide is destroyed, and only then the carbonyl can come into direct contact with the walls and form a coherent deposit of metal. Therefore, the whirling or stirring should be so thorough as to effect a good equalization of heat Within the vessel, but not so strong as to result in a destruction of the protective layer of carbon monoxide.

Even when employing the aforesaid measures for facilitating the supply of heat to the carbonyl to be decomposed, only 'a cer-v tain amount of carbonyl can be decomposed per unit of time in a furnace of a given size. The same disadvantage is inherent with another known process for the decomposition of metal carbonyls to produce metal powders which consists in bringing the said carbonyls into contact with hot inert gases. This meth- 0d of working has the additional disadvantage that large amounts of hot gases are to be employed in consequence of the low specific heat of gases in order to supply the necessary heat and accordingly the metals produced are distributed in large amounts of gases and difficulties arise in the separation of the metals.

We have now found that the efliciency of the process in which the metal carbonyl is thermally decomposed by introducing it, diluted, if desired, with inert gases, into a heated vessel in such a manner that the decomposition takes place substantially in the hot free space of the vessel instead of by contact with the hot walls of the vessel can be substantially increased without the aforesaid disadvantages by supplying the heat necessary for the decomposition partly from outside through the walls of the decomposition vessel and partly by means of hot gases or vapors or finely divided solids supplied to the interior of the vessel. This manner of working renders it possible on the one hand to avoid overheating the walls of the furnace and on the other hand to avoid too great a dilution of the carbonyl with inert gases and also to increase the yield of metal powder obtained per unit of time and per {)mit of volume of the decomposition cham- The walls of the vessel may be heated in any known manner for example by electrical resistance heating or by means of a hollow jacket surrounding the decomposition chamber through which heating gases circulate. As the source of heat in the interior, introduced hot gases which are preferably employed in a cycle may be emp oyed as for example heated carbon monoxide. Other heated substances such for example as liquid or solid substances in a finely divided state may be introduced into the decomposition chamber, and in this connection, substances with the greatest possible specific heat are the most suitable. As finely divided substances introduced into the interior in a heated condition preferably such are employed as may remain in the metal powder produced, for example the same metal in a finely divided state as is produced in the process, or those metals wit-h which the metal produced by the decomposition of its metal carbonyl is afterwards to be alloyed. stances in a. fine division which can afterwards readily be removed, for example by dilution, may also be used. Moreover by the introduction at a suitable place in the vessel of an amount of air, or better still of oxygen, insuificient for the complete oxidation of the substances to be decomposed or of the substances formed by the decomposition, an inverted flame may be used as the source of heat. Furthermore the metal particles themselves which are formed by the decomposition may be employed in many cases for supplying heat in the interior, this being effected by heating them by electrical induction.

The introduction of the vaporous or atomized carbonyl preferably takes place in the centre of the upper end of the decom osition chamber, which latter preferably as the form of a vertical cylinder.

In this process a certain whirling or stirring effect may be obtained in some cases due to the supply of heat in the interior, but it may be advantageous to employ additional whirling or stirring in the manner hereinbefore described, or to heat the walls of the vessel to a temperature substantially higher than the temperature in the free space of the vessel, or to employ both, whirling or stirring and strong heating of the walls of the vessel.

Of course, the most favorable conditions of working depend on the particular circumstances in each case, for example on the capacity and heating surface of the decomposition vessel, on the amount of carbonyl to be converted per unit of time, and on the degree of fineness and the carbon content, the product should have. They cannot, therefore, be predicted in a precise manner, but everybody skilled in the art will be able to apply the principles set forth in the foregoing to the best economy and advantage.

he processaccording to the present invention is particularly valuable for the production of finely divided iron by the thermal decomposition of iron carbonyl.

An apparatus suitable for carrying out the process according to the present invention is diagrammatically illustrated in vertical section in theaccompanying drawing. In the Other solid subsaid apparatus liquid iron carbonyl is supfinely divided iron and carbon monoxide.-

The iron is carried along with the gas and separated in the chambers K K and K, from which it can be withdrawn by means of worm conveyors C arranged in the lower part thereof. A portion of the carbon monoxide set free during the decomposition is introduced by means of the circulation pump M into an electric heating device N and is then returned into the decomposition vessel H by means of a pipe 0. In order to supply the hot carbon monoxide uniformly to the interrior of the vessel H, the pipe 0 is connected with an annular tube P arranged in the upper part of the decomposition vessel H and provided with a large number of fine holes. The amount of cabon monoxide which is maintained. in circulation can be controlled by means of the pump M and its temperature by means of the heating device N. The remainder of the carbon monoxide which is not circulated throu h the apparatus is withdrawn by way 05a pipe L.

What we claim is 1. In the production of finely divided metals by thermal decomposition of metal carbonyls in the hot free space of a heated ves sel, the step of supplying the heat necessary for the decomposition partly from outside through the walls of the decomposition vessel and partly in the interior of the vessel.

2. In the production of finely divided metals by thermal decomposition of metal carbonyls in the hot free space of a heated vessel, the step of supplying the heat necessary 4 for the decomposition partly from outside through the walls of the decomposition vessel and partly in the interior of the vessel, while subjecting the substances present in Elie decomposition vessel to a whirling mo- 3. In the production of finely divided metals by thermal decomposition of metal carbonyls at temperatures between about 100 and 400 C. in the hot free space of a heated vessel, the step of supplying the heat necessary for the decomposition partly from outside through the walls of the decomposition vessel and partly in the interior of the vessel, the temperatureof the walls of the vessel being kept substantially higher than the temperature in the interior of the vessel.

4. In the production of finely divided metals by thermal decomposition of metal carbonyls at temperatures between about 100 and l00 C. in the hot free space of a heated vessel, the step of supplying the heat necessary for the decomposition partly from outside through thewalls of the decomposition vessel and partly in the interior or" the vessel, while subjecting the substances present in the decomposition vessel to a whirling motion, the temperature of the walls of the vessel being kept substantially higher than the temperature in the interior of the vessel.

5. In the production of finely divided iron by thermal decomposition of iron carbonyl in the hot free space of a heated vessel, the step of supplying the heat necessary for the decomposition partly from outside through the walls of the decomposition vessel and partly in the interior of the vessel.

6. In the production of finely divided iron by thermal decomposition of iron carbonyl in the hot I'ree space of a heated vessel, the step of-supplying the heat necessary for the decomposition partly from outside through the walls of the decomposition vessel an partly in the interior of the vessel, while subjecting the substances present in the decomposition vessel to a whirling motion.

7. In the production of finely divided iron by thermal decomposition of iron carbonyl at temperatures between about 100 and 400 C. in the hot free space of a heated vessel, the step of supplying the heat necessary for the decomposition partly from outside through the walls of the decomposition vessel and partly in the interior of the vessel, the temperature of the walls of the vessel being kept substantially higher than the temperature in the interior of the vessel.

8. In the production of finely divided iron by thermal decomposition of iron carbonyl at temperatures between about 100 and 400 C. in the hot free space of a heated vessel, the step of supplying the heat necessary for the decomposition partly from outside through the walls of the decomposition vessel and artly in the interior of the vessel,while sub- 1ecting the substances present in the decomposition vessel to a whirling motion, the temperature of the walls of the vessel being kept substantially higher than the'temperature in the interior of the vessel.

In testimony whereof we have hereunto set doc 

